Disk drives are widely used in computers, consumer electronics and data processing systems for storing information in digital form. The disk drive typically includes one or more storage disks and one or more head suspension assemblies. Each head suspension assembly includes a slider assembly which has an air bearing surface, a leading edge, a trailing edge and a read/write head positioned near the trailing edge. The read/write head transfers information to and from the storage disk. Rotation of the storage disk causes the slider assembly to ride on an air-supported journal bearing (also referred to as an “air bearing”) so that the read/write head is at a distance from the storage disk that is commonly referred to as a “head-to-disk spacing”.
Because today's disk drives utilize storage disks having increasingly high densities of data tracks, decreasing the head-to-disk spacing has become of great importance. However, this desire for a very small head-to-disk spacing must be balanced with tribological concerns in order to avoid damage to the read/write head and/or the storage disk, as well as loss of data.
Maintaining a relatively small and consistent head-to-disk spacing is further complicated by other factors. In particular, the read/write head includes a write head having electrical conduction path(s), generally referred to as a “write element”. During a write operation, the electrical resistance of the electrical circuitry in the write element generates heat in and around the read/write head. The extent and rate of heating depends upon a multiplicity of factors including but not limited to the level of current directed to the write element, the types of materials used in the construction of the write element, and the sizes and geometries of various features within the slider assembly. A temperature increase causes thermal expansion of portions of the slider assembly toward the storage disk, known as write pole tip protrusion (“WPTP”). In addition, environmental temperature increases within the disk drive that are independent of heating the write element and that act on a more global scale can also result in environmental pole tip protrusion (“EPTP”) toward the storage disk. If pole tip protrusion is excessive, the slider assembly can unintentionally contact the storage disk (“head-to-disk contact”), causing off-track writing, degraded data transfer rates, damage to the slider assembly, damage to the storage disk and/or a permanent loss of data.
Conversely, a temperature decrease in the drive will induce the opposite effect on the EPTP—the pole tips will retract from the disk. Such retraction can degrade the performance of the reading and writing process since larger spacing can generally degrade the information transfer to and/or from the disk.
Moreover, in conventional disk drives, the slider assembly is typically formed from ceramic materials such as alumina titanium carbide (Al2O3—TiC), and can be secured to a suspension assembly that is typically formed from metal materials such as stainless steel. Environmental heat that is generated within the disk drive can cause thermal expansion of the suspension assembly, as well as the slider assembly. However, stainless steel has a coefficient of thermal expansion that is approximately 2.5 times greater than the coefficient of thermal expansion of Al2O3—TiC. Because of this disparity, thermal expansion of the stainless steel occurs to a greater extent than thermal expansion of the slider assembly. Consequently, concavity of the slider assembly often occurs in a direction from the leading edge to the trailing edge, also referred to herein as the “crown” direction as temperature within the disk drive increases. This concavity results in the trailing edge, and thus the read/write head, moving closer to the storage disk, further risking or actually causing unwanted head-to-disk contact. Further, if the temperature of the read/write head decreases, the opposite effect can occur, e.g. the slider crown moves in direction of being more convex (or at least less concave) and this increases head-to-disk spacing with potentially adverse implications, as indicated above.